There are professional and government agencies which publish standards for "purified water" for Good Manufacturing Practices (GMP) for commercial laboratories, universities, hospitals, pharmaceutical companies or electronics manufacturers. Thus the term "purified water" has different definitions, depending on which group or agencies' standards are being followed.
The common denominator within the standards is the requirement that the process used to treat and distribute the water must consistently deliver water that meets the standards required by the end users. Commercial laboratory, GMP, or pharmaceutical water purifying systems have strategically positioned water sampling valves and water quality analytical instruments that are used to monitor the systems' performance and the water purity at various stages of processing, and at the use points.
Reverse osmosis water treatment systems are standard primary treatments of choice because of their capability to reduce dissolved salts by as much as 99.5 percent and to reduce suspended matter and microorganisms by over 99.5 percent. If a standard requires only moderate levels of purity, reverse osmosis with properly treated make-up feed water may suffice. If a standard requires higher levels of purities, additional treatment can be employed, such as a second RO in series with the first one (double pass), deionizing resins, and ultraviolet treatment, for example. Purified water must be stored and distributed through piping, tanks, pumps, and fittings that do not contaminate it. Entire storage and distribution systems must be compatible with various harsh cleaning chemicals, sanitizing agents or with water temperatures of up to 90.degree. C. (194.degree. F.), if heat is employed to sanitize them.
A reverse osmosis module known to the art consists of a semi-permeable membrane within a pressure vessel that allows some water to pass through the membrane when the water pressure is at a controlled point. As some of the water passes through the membrane, the suspended matter, microorganisms, and dissolved solids in the remaining water increase (concentrate). As they increase, some may settle or precipitate on the surface of the membrane, forming a deposit that can reduce the flow and the rated performance of the module.
During the off cycles when the make-up water and the pump are shut off; the concentrated material that has deposited during the operating cycles can solidify and it can form a scale. Bacteria proliferate during static periods and they colonize on the downstream surface of the membranes. By the process of osmosis, dissolved salts pass through the membranes thus contaminating the permeate side whenever a conventional system is in off-cycle modes.
When the operating flux (flow) through a module decreases by 10 to 15 percent, or if the rejection of dissolved solids drops by 10 percent, the module must be chemically cleaned with combinations of approved alkali and then by acid solutions and rinsed until the rated performance is restored. When microorganisms form colonies within the modules and contaminate the purified water, the modules must be cleaned and then sanitized with an agent or agents approved by the module manufacturer. The downtime is considerable. Replacing the fouled membranes is sometimes necessary, when getting the system operational is essential to the users of the purified water and insufficient time is available for cleaning and sanitizing.
Cleaning and sanitizing RO modules requires shutting down the water purifying process for several hours or days, which adversely impacts on those who require purified water for their activities. Therefore, the procedure is often times postponed for convenience, thus causing the contamination problems to increase and the performance standard to decrease beyond membrane manufacturers' recommendations. If the purified water has contamination levels that exceed the users' specifications or recommended levels, the water may not be used for manufacturing until the purity is restored and has passed analytical tests which may require several days to perform. Microbiological problems within RO purified water systems are universally known of and acknowledged in laboratory and GMP manufacturing industries because the published standards, in order to be obtained, require that microbiological tests of the purified water be performed and recorded. They clearly show that frequent cleaning and sanitizing is required in order to comply with standard specifications.
To remedy some of the design deficiencies of standard reverse osmosis water treatment systems, various attempts and inventions have been made. Some of the water treatment systems are disclosed in the following patents, which are not intended to be all-inclusive but only exemplary of the prior art.
______________________________________ U.S. Pat. No. Date Title ______________________________________ 4,629,568 Dec. 16, 1986 Fluid Treatment System 4,773,993 Sep. 27, 1988 Apparatus for Purifying and Dispensing Water with Stagnation Preventing Means 4,784,771 Nov. 15, 1988 Method and Apparatus for Purifying Fluids 5,647,973 Jul. 15, 1997 Reverse Osmosis Filtration System with Concentrate Recycling Controlled by Upstream Conductivity ______________________________________
An automatic cleaning system for a filter is shown in the following U.S. Pat. No.: 4,921,610 May 1, 1990 Cleaning of Hollow Fibre Filters
Accordingly one object of the invention is to provide an improved cleaning and sanitizing system for a reverse osmosis water purification system which operates automatically and unattended.